U.S. patent application number 11/596359 was filed with the patent office on 2007-10-18 for mobile telephone handset with capacitive radio frequency path between first and second conductive components thereof.
Invention is credited to Brian Collins.
Application Number | 20070243913 11/596359 |
Document ID | / |
Family ID | 32527027 |
Filed Date | 2007-10-18 |
United States Patent
Application |
20070243913 |
Kind Code |
A1 |
Collins; Brian |
October 18, 2007 |
Mobile Telephone Handset with Capacitive Radio Frequency Path
Between First and Second Conductive Components Thereof
Abstract
There is disclosed a mobile telephone handset having a casing
including first and second components that slide relative to each
other between a closed and an open configuration of the handset.
The first and second components are interconnected by an
electrically conductive connector, and facing surfaces of the first
and second components are provided with electrically conductive
surfaces or coatings that define an additional capacitive radio
frequency path between the first and second components. The
additional capacitive radio frequency path helps to divert radio
frequency currents that might otherwise flow through the
electrically conductive connector and thereby adversely affect
performance of the handset.
Inventors: |
Collins; Brian; (Cambridge,
GB) |
Correspondence
Address: |
PEARL COHEN ZEDEK LATZER, LLP
1500 BROADWAY 12TH FLOOR
NEW YORK
NY
10036
US
|
Family ID: |
32527027 |
Appl. No.: |
11/596359 |
Filed: |
May 13, 2005 |
PCT Filed: |
May 13, 2005 |
PCT NO: |
PCT/GB05/01840 |
371 Date: |
November 14, 2006 |
Current U.S.
Class: |
455/575.4 |
Current CPC
Class: |
H04M 1/0237 20130101;
H04B 1/3833 20130101 |
Class at
Publication: |
455/575.4 |
International
Class: |
H04M 1/02 20060101
H04M001/02 |
Foreign Application Data
Date |
Code |
Application Number |
May 14, 2004 |
GB |
0410760.3 |
Claims
1. A mobile telephone handset comprising: a casing comprising first
and second components that slide relative to each other between a
closed and an open configuration of the handset, wherein the first
and second components are interconnected by an electrically
conductive connector, and wherein facing surfaces of the first and
second components comprise electrically conductive surfaces that
define an additional capacitive radio frequency path between the
first and second components.
2. A handset as claimed in claim 1, wherein an external side of at
least one of said facing surfaces with comprises an electrically
conductive surface.
3. A handset as claimed in claim 2, wherein the electrically
conductive surface comprises an insulating coating or layer.
4. A handset as claimed in claim 1, wherein an internal side of at
least one of said facing surfaces is provided with an electrically
conductive surface.
5. A handset as claimed in claim 1, wherein the conductive surfaces
are not provided at a location of the electrically conductive
connector.
6. A handset as claimed in claim 1, wherein the conductive surfaces
are electrically grounded.
7. A handset as claimed in claim 6, wherein the conductive surfaces
are electrically connected to an electrical groundplane or ground
connector provided in a handset component.
8. A handset as claimed in claim 2, wherein the conductive surfaces
or coatings are smooth.
9. A handset as claimed in claim 2, wherein at least one of the
conductive surfaces is grooved or ridged.
10. A handset as claimed in claim 2, wherein the conductive
surfaces are provided on spaced apart regions of each handset
component.
11. A handset as claimed in claim 10, wherein the spaced apart
regions are located on either side of a central sliding
mechanism.
12. A handset as claimed in claim 1, wherein the first and second
handset components are configured to slide relative to each other
along a single longitudinal axis.
13. A handset as claimed in claim 1, wherein the first and second
handset components are configured to slide rotatably about an axis
of rotation.
14. (canceled)
15. The handset of claim 1, wherein the electrically conductive
surfaces comprise coatings.
Description
[0001] The present invention relates to a mobile telephone handset,
and in particular to a handset comprising two parts that slide
relative to each other when a user converts the handset between an
"open" and a "closed" configuration.
[0002] Handsets for mobile telephone systems are manufactured in a
number of different physical configurations. These include single
rigid `bar-phones`, folding or `clamshell` phones and two-piece
`slider phones`. The present invention relates to slider phones. It
will be appreciated that the term `slider phones` encompasses both
the type of handset where the two parts slide laterally with
respect to each other, as well as those types where one part twists
relative to the other in a plane generally parallel thereto, these
types sometime being known as `swing phones`.
[0003] A typical slider phone handset is shown in FIG. 1.
[0004] With reference to FIG. 1, the handset comprises a first
component (1) typically containing the display (3), and a second
component (2) typically containing the keypad and many of the
electronic circuits required to provide the functionality of the
handset. When in the closed configuration, the keypad is protected
by the first component of the handset.
[0005] An antenna (4) is typically located at the end of the second
component where it may be located externally or within the second
component. The two components of the handset are typically
connected by a connection means (5), typically a flexible printed
circuit which carries a large number of conductors whose function
is to control the display and other devices on the first component
of the handset.
[0006] A limitation of this design is that when the antenna is
driven by the output of the handset, radio frequency currents are
caused to flow in the connection means. These currents contribute
little to the signal radiated from the handset and contribute only
to loss in the resistance of the interconnecting conductors. The
input impedance of the antenna varies substantially between the
open and closed configurations of the handset.
[0007] In the example of FIG. 1, the connection means may
accommodate typically between 30 and 50 individual conductor traces
(printed circuit conductors), including some traces whose function
is to interconnect the groundplanes of the two components of the
handset. The connection means is typically between 50 mm and 80 mm
long. Each individual conductor has substantial resistance and
inductance, and a capacitance exists between the conductors and the
faces of the components of the handset.
[0008] For practical mechanical reasons, it is not generally
possible to incorporate a wide, low-resistance ground conductor
into the connection means. This is because the spacing between the
two components of the handset is small, and a flexible printed
circuit with a wide copper conductor is not sufficiently flexible
to be accommodated within the spacing. Moreover, repeated flexing
of the wide copper conductor as the handset is opened and closed
will lead to cracking and failure.
[0009] In order to mitigate the effects of the interconnecting
connections it is necessary either to prevent the flow of RF
currents between the handset components, or to ensure that the
currents are provided with an alternative current path and do not
flow through the lossy interconnections described above.
[0010] It is known from EP 0 622 864 (Casio) to provide a rigid
`bar-phone` or a `clamshell` phone including first and second metal
housings with an antenna mounted on the first housing, and a
conductive electrical connection between components housed in the
first housing with components housed in the second housing. A
discrete control element is provided between the first and second
metal housings so as to control a distribution of high frequency
currents flowing through the first and second housings. The control
element, which is in the form of a small chip, includes one or more
of a resistor, a capacitor, a coil and/or a diode, and is connected
by wire between the first and second housings. By varying the
impedance of the control element, it is possible to vary the
characteristics of the antenna mounted on the first housing. This
is because varying the impedance of the control element serves to
control the distribution of the high frequency currents flowing in
the housings, which generate electromagnetic fields that can
interfere with the performance of the antenna. This arrangement
does not seek to control high frequency currents from interfering
with currents flowing in the conductive electrical connection.
Indeed, the conductive electrical connection is specifically
designed so that the first and second housings are not
shortcircuited thereby. This arrangement is not possible in
handsets where groundplanes housed in first and second housings are
interconnected with each other.
[0011] Embodiments of the present invention relate to means whereby
a low-impedance capacitive current path can be provided between the
handset components, reducing the level of radio frequency currents
that flow in the interconnecting conductors and thereby reducing
associated losses and improving the stability of the performance of
the antenna when the handset is opened and closed. At the same
time, an impedance of the alternative path through the
interconnecting conductors may be increased.
[0012] According to the present invention, there is provided a
mobile telephone handset having a casing comprising first and
second components that slide relative to each other between a
closed and an open configuration of the handset, wherein the first
and second components are interconnected by an electrically
conductive connector, and wherein facing surfaces of the first and
second components are provided with electrically conductive
surfaces or coatings that define an additional capacitive radio
frequency path between the first and second components.
[0013] In one embodiment of the invention, facing surfaces of the
two components are provided with electrically conductive surfaces
or coatings (e.g. metallised paint) on their outer, respectively
proximate faces. An insulating coating or lamina is preferably
placed between the facing surfaces to avoid possible physical
contact which might cause electrical noise or physical damage to
the coatings.
[0014] Alternatively or in addition, the conductive surface or
coating may be provided inside one or both components of the
handset, for example on inner sides of the facing surfaces. In this
embodiment, an additional insulating layer need not be provided,
since the conductive surfaces cannot electrically contact each
other.
[0015] The conductive surface or coating is advantageously not
provided in the region of the interconnecting electrically
conductive connector, thereby helping to reduce or minimise the
capacitance between the circuit traces and the coating. This
ensures that the impedance presented at the ends of the
interconnections is as high as possible compared with the low
impedance of the capacitive path provided directly between the
facing surfaces of the components.
[0016] Advantageously, each of the conductive surfaces or coatings
is electrically grounded, for example by way of a connection to an
electrical groundplane or ground connector provided for circuit
components in the handset.
[0017] The conductive surfaces or coatings may be provided on
spaced apart regions of each handset component, and may be located
on either side of a central sliding mechanism.
[0018] For a better understanding of the present invention and to
show how it may be carried into effect, reference shall now be made
by way of example to the accompanying drawings, in which:
[0019] FIG. 1 shows a slider-type telephone handset in closed and
open configurations;
[0020] FIG. 2 shows a slider-type telephone handset of an
embodiment of the present invention;
[0021] FIG. 3 shows a possible modification to the embodiment of
FIG. 2;
[0022] FIG. 4 shows return loss results for a first antenna fitted
to an embodiment of the present invention;
[0023] FIG. 5 shows return loss results for a second antenna fitted
to an embodiment of the present invention;
[0024] FIG. 6 shows return loss results for a third antenna fitted
to an embodiment of the present invention;
[0025] FIG. 7 shows measured terminal efficiencies for the first
antenna fitted to an embodiment of the present invention;
[0026] FIG. 8 shows measured terminal efficiencies for the second
antenna fitted to an embodiment of the present invention;
[0027] FIG. 9 shows measured terminal efficiencies for the third
antenna fitted to an embodiment of the present invention; and
[0028] FIG. 10 shows a comparison of return loss for an embodiment
of the invention with the electrically conductive connector
respectively connected and disconnected to a printed circuit board
in one of the handset components.
[0029] The invention is described by reference to FIG. 2 which is a
view from an end of the handset. As in FIG. 1, the two components
of the handset and its enclosing case mouldings are referred to for
convenience as `upper` 1, and `lower` 2. The interconnecting
flexible circuit 5 lies in the centre of the region between the
handset components and is looped in the same manner as that of FIG.
1, allowing longitudinal axial motion of the components as
before.
[0030] Regions of both upper 1 and lower 2 case moulding outside
the area occupied by the flexible circuit 5 are made of conducting
material or are coated with a conductive coating 6, 7, 8, 9. This
conductive surface is preferably applied on both the inside and the
outside of the case mouldings. The faces to which the conductive
surface is provided. may be flat as shown or may carry
corresponding longitudinal curves or ridges, provided that an
average separation `s` between the surfaces is maintained to be as
small as practicable. Preferably, insulating laminae 16, 17 are
placed between the conductive surfaces to prevent intermittent
contact causing undesirable electrical effects. Such laminae may be
formed from insulating membranes or the proximate surfaces may be
over-painted with conventional insulating paint.
[0031] The conductive coatings are conductively connected to the
ground planes of the internal printed circuit boards (PCBs) 10, 11
by conductive means 12, 13, 14, 15. The components of the handset
are maintained at a substantially constant spacing by sliding means
18, 19. Such sliding means may be of conductive or non-conductive
parts and may accommodate a spring or over-centre action to provide
smooth and positive action; their design is well known and is not
constrained by the application of the present invention.
[0032] As shown in FIG. 3, to increase the space available for the
electrical interconnection between the handset components, the
central region of one or both components 1, 2 may optionally be
provided with one or more recesses 20 to provide increased
accommodation for the flexible connection 5.
[0033] Three different antennas were optimised in turn in place on
one handset. In each case the optimisation was carried out in the
open position and the input VSWR was measured in both open and
closed states. The terminal efficiency of the same test phone was
then measured in a SATIMO STARGATE 64 spherical near-field chamber
with the phone in both open and closed states with each of the
three antennas fitted in turn.
[0034] Three ceramic hybrid antennas with different radiator
geometries were optimised to give optimum return loss in the phone
open configuration. The resonant frequencies of the antennas were
then offset slightly to balance the performance at the band edges
in the open and closed states. The bandwidth achieved for all the
configurations was very similar. In the closed state there is a
shift in the frequency of the optimum match in the 900 MHz band,
while in the 1800 MHz band closing the phone creates a much wider
match bandwidth and the match in the DSC band is relatively
unchanged.
[0035] The return loss/frequency curves for the three antennas are
shown in FIGS. 4, 5 and 6. Each Figure shows the results with the
phone in the open and closed positions.
[0036] The antennas display very similar return loss/frequency
characteristics. The frequency of optimum impedance match in the
GSM900 band falls when the handset is closed, while at the 1800 MHz
the match is less affected and a variety of additional resonances
appear between the two operating frequency bands.
[0037] The optimisation of the antenna geometries started from very
different points, so it is interesting that all the results are so
similar. When the handset is closed the return loss in the 900 MHz
band is greatest at the low end of the band, so it would be
expected that the efficiency will be highest at the lower end of
the band, while in the open state it would be expected to be
greatest at the high end of the band
[0038] The results of the efficiency measurements are shown in
FIGS. 7, 8 and 9. A sleeve balun of an appropriate length was
fitted close to the handset for all measurements to reduce stray
radiation from connecting cables. The terminal efficiency includes
the reflection loss at the antenna terminals and would be expected
to be lower for conditions in which the antenna input return loss
is small. In each case the result with the handset open is shown in
light grey, while that in the closed position is shown in dark
grey.
[0039] There are several very interesting features of these
results:
[0040] Version 2.1 has very different characteristics in the 1800
MHz band than the other two antennas, but in the 900 MHz band the
efficiency results and the efficiency/frequency relationships are
strikingly similar.
[0041] The return loss results (FIG. 4) confirm that the best match
in the closed position is at the bottom of the 900 MHz band, yet
the efficiency is always lowest at this frequency.
[0042] The mean return loss in the 900 MHz band is very similar in
open and closed positions, yet the efficiency in the closed
position is very much lower.
[0043] These results suggest that the efficiency results in the 900
MHz band are a function of the behaviour of the phone rather than
of the antenna.
[0044] To examine this possibility the antenna with the highest
mean efficiency (v3.2) was re-fitted to the handset and the end of
the linking flexible PCB (the electrically conductive connector)
was disconnected from the rear of the main PCB in the handset. The
return loss was then re-measured with the result shown in FIG.
10.
[0045] It can be seen that the match in the 900 MHz band almost
completely disappears when the flexible PCB is disconnected. This
clearly indicates that the match at 900 MHz is influenced very
heavily by currents flowing in the flexible PCB, and the poor
efficiency in the 900 MHz band suggests that these currents mostly
contribute loss.
[0046] In conclusion, it has been demonstrated that the
interconnections between the components of a slider phone handset
have a major effect on the efficiency which can be achieved.
[0047] The preferred features of the invention are applicable to
all aspects of the invention and may be used in any possible
combination.
[0048] Throughout the description and claims of this specification,
the words "comprise" and "contain" and variations of the words, for
example "comprising" and "comprises", mean "including but not
limited to", and are not intended to (and do not) exclude other
components, integers, moieties, additives or steps.
* * * * *